1. Field of the Invention
The present invention relates to transmission power control for a communication channel in a radio communications system.
2. Description of the Related Art
In radio communications systems, considerations have been made on the transmission of a variety of contents including video clips, multimedia data, games, streaming videos and the like. Commercialization of such a transmission system entails a reduction in delay in uplink communications, an enlargement of a coverage area, and an improvement in throughput in the radio communications systems. The introduction of communications on uplink high-rate communication channels have been under investigation as a communications scheme suitable for such systems. Such a communication scheme is defined in a standard such as 3GPP TR 25.896 V6.0 by 3GPP (3rd Generation Partnership Project).
Technologies have been desired for realizing a service using uplink high-rate channels, as mentioned above, without affecting existing communications and services on data communication channels.
The transmission power on an uplink channel in a radio communication system is controlled in accordance with an outer-loop power control method and an inner-loop control method. These transmission power controls are defined, for example, in 3GPP TS 25.214 V3.12.0. Technologies have been desired for realizing services using uplink high-rate channels without affecting existing communications and services through data communication channels while utilizing existing systems which are operated under such outer-loop power control or inner-loop power control.
A change in a propagation path condition caused by a communication channel initiated at a later time, such as the uplink high-rate channel, may affect the reception quality of other existing uplink channels which have already been in service. For example, as shown in FIG. 1, the start of a later communication through a communication channel can cause an increase in interfering power to suddenly degrade the reception quality (for example, SIR: Signal to Interference Ratio) of an earlier communication. Also, a degradation in the reception quality of an earlier uplink communication channel can cause a disconnection of an earlier communication through the uplink channel. Alternatively, a degradation in the reception quality of an earlier communication channel can be recovered by the transmission power control in some cases, but an earlier communication through the channel can be disconnected when the reception quality falls short of a signal quality required for communications.
A technology relating to a downlink communication in a radio communications system is described in JP, P2002-325063A, where a cellular system increases a target reception SIR for an uplink data channel by a predetermined offset when a downlink high-rate channel is transmitted. Also, a technology relating to radio communications systems is described in JP, P2003-199173A in which quality information is transmitted, in a mobile communications system, from a mobile station to a base station only when it is required. Further, JP, 8-191418A discloses a call acceptance control method which rejects the acceptance of a new call when it is predicted that there is a mobile station which cannot satisfy a predetermined communication quality at the time the new call is received.
As described above, in a conventional radio communications system in which a plurality of uplink channels can be set, changes in situation or condition a propagation path caused by a communication channel initiated at a later time, such as the uplink high-rate channel, may affect the reception quality of other existing uplink channels which have already been in service. Also, a degraded reception quality of an earlier uplink channel can affect a communication condition, for example, the communication quality on the earlier uplink channel. A degraded reception quality of an earlier uplink channel can cause a disconnection of a communication through the earlier uplink channel.
Also, in an attempt to reduce the influence on an earlier uplink communication channel exerted by changes in condition or situation on a propagation path caused by a communication channel initiated at a later time, such as the uplink high-rate channel, the transmission power can be excessively increased for the earlier uplink channel, or the reception quality can be excessively improved for the earlier uplink channel.
Even in a situation where the outer-loop power control is conducted for an earlier uplink channel, a need exists for reducing the influence on communications on the earlier uplink channel exerted by changes in condition or situation on a propagation path caused by a communication channel initiated at a later time, such as a uplink high-rate channel. Also, in a situation in which the outer-loop power control is conducted for the earlier uplink channel as mentioned above, when an attempt is made to reduce the influence on the earlier uplink channel exerted by changes in condition or situation on the propagation path caused by the communication channel initiated at a later time, such as the uplink high-rate channel, the transmission power can be excessively increased for the earlier uplink channel, or the reception quality can be excessively improved for the earlier uplink channel.